1. Field of the Invention
The present invention relates to a light-emitting semiconductor diode (LED) and a semiconductor laser diode which use gallium nitride (GaN) compound with a double hetero-junction structure, and which emit visible short wave rays in the blue to violet region and also in the ultraviolet region of the optical spectrum.
2. Description of Background Information
A conventional LED using a GaN compound semiconductor has been known to have a structure similar to that shown in FIG. 1. It has a sapphire substrate on which GaN compound semiconductor layers are epitaxially grown. Since the light from the emission layer of the LED is emitted equally in all directions, only a fraction of the emitted light, which is taken out through an outlet port, has been utilized. Most of the emission light has been wasted, resulting in low luminous intensity.
A conventional laser diode disclosed in U.S. Pat. No. 5,247,533 utilizes a sapphire substrate on which a double hetero-junction structure is epitaxially grown.
The double hetero-junction structure comprises indium gallium aluminum (InGaAlN) compound semiconductor layers, satisfying the formula (Al.sub.x Ga.sub.1-x).sub.y In.sub.1-y N inclusive of 0.ltoreq.x.ltoreq.1 and 0.ltoreq.y.ltoreq.1, and an active layer not doped with any impurities which are epitaxially grown. Since the laser diode utilizes a sapphire substrate whose crystalline characteristic is different from that of the active layer, it is difficult to obtain cleavage sufficient to function as an effective mirror for the edge surface of the active layer. Consequently, the conventional GaN laser diode has a low oscillation efficiency.